Reactions in which none of the atoms undergo a change in oxidation number are called metathesis reactions. Consider the reaction between a carboxylic acid and an amine, for example.

Or the reaction between an alcohol and hydrogen bromide.

These are metathesis reactions because there is no change in the oxidation number of any atom in either reaction.

The oxidation numbers of the carbon atoms in a variety of compounds are given in Table 3.

The oxidation numbers given in Table 3 can be used to classify organic reactions as either oxidation-reduction reactions or metathesis reactions. Because electrons are neither created nor destroyed, oxidation cannot occur in the absence of reduction, or vice versa. It is often useful, however, to focus attention on one component of the reaction and ask: Is that substance oxidized or reduced? Assigning oxidation numbers to the individual carbon atoms in a complex molecule can be difficult. Fortunately, there is another way to recognize oxidation-reduction reactions in organic chemistry.

Oxidation occurs when hydrogen atoms are removed from a carbon atom or when an oxygen atom is added to a carbon atom. Reduction occurs when hydrogen

Table 3 Typical Oxidation Numbers of Carbon

Functional group


Oxidation number of carbon in the example


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